Addition Rate Constants of Phosphorus- and Carboncentered Radicals to Double Bond of Monomers as Studied by a Pulsed EPR Method
Addition Rate Constants of Phosphorus- and Carboncentered Radicals to Double Bond of Monomers as Studied by a Pulsed EPR Method
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脉冲 EPR 方法研究磷和碳中心自由基对单体双键的加成速率常数
DOI：
10.1021/acs.jpca.5b04464
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发表时间：
2015
期刊：
影响因子：
2.9
通讯作者：
and Akio Kawai
中科院分区：
文献类型：
--
作者：
H. Takahashi;Y. Marushima;K. Shibuya;and Akio Kawai
用时间分辨(TR-)和脉冲电子顺磁共振(EPR)光谱方法研究了单体的双键加成反应，这在光聚合的早期阶段是重要的。一个以磷为中心的自由基和三个以碳为中心的自由基攻击几个单体的反应已被采用。通过分析记录的TR-EPR谱确定中间自由基，并用Weber和Turro提出的电子自旋回波检测方法确定反应速率常数[J.Phys]。化学。A，2003,107(18)，3326−3334]。量子化学计算表明，通过引入“热效应”和“极性效应”两个因素来控制活化势垒高度，可以很好地解释加成反应的速率常数。结果表明，对于某些单体，含磷自由基的速率常数大于含碳自由基的速率常数。在频率因子和活化势垒的基础上讨论了速率常数的不同，它们都受自由基中心原子的影响。
Addition reaction of a radical to the double bond of a monomer, which is important at early stage of photopolymerization, has been studied by time-resolved (TR-) and pulsed electron paramagnetic resonance (EPR) spectroscopic methods. Reactions of one phosphorus-centered and three carbon-centered radicals attacking to several monomers have been employed. Intermediate radicals were identified by analyzing the recorded TR-EPR spectra, and the reaction rate constants were determined by the electron spin–echo detection method proposed by Weber and Turro [J. Phys. Chem. A, 2003, 107 (18), 3326−3334]. The quantum chemical calculation shows that the rate constants for the addition reactions are well-explained by introducing two factors of “enthalpy effect” and “polar effect” to control the activation barrier height. It was observed that the rate constants of the phosphorus-centered radical were larger than those of carbon-centered radicals for some monomers. The difference in the rate constants was argued on the basis of frequency factor and activation barrier both of which are influenced by an atom of radical center.